Heretofore, in battery cases for sealing strongly alkaline solutions of alkali-manganese batteries as primary batteries or nickel-cadmium batteries as secondary batteries and, further, nickel hydrogen batteries for which growth of demand has been expected in recent years as new secondary batteries, a so-called post-plating method of applying barrel plating after pressing cold rolled steel sheets, or a so-called pre-plating method of pressing a nickel plated steel sheets into a battery case have been adopted, for which many proposals have been made for the improvement and the present inventors have also proposed an excellent surface treated steel sheet for battery cases with low internal resistance (International Publication No. WO95/11527).
Further, in recent years, as a press forming method for battery cases, a DI (drawing and ironing) forming method has also been used as a wall thinning method instead of a multi-stage deep drawing method for increasing the battery capacity (JP-B No. 7-99686). The DI forming method or DTR (drawing thin and redraw) forming method can fill more positive electrode and negative electrode active substances by as much as the additional volume created by the side wall being thinner than the bottom, to increase the capacity of the battery, as well as also provide a merit capable of improving the pressure proofness of the battery since the case bottom is thick.
By the way, while the DI forming method or the DTR forming method is a forming method effective to the increase of the battery capacity as described above, since the deformation resistance of a material is larger compared that with the existent multi-stage deep draw forming method in view of the forming ability, it involves a disadvantage with respect to the continuous forming property.
Further, it has been required for alkali-manganese batteries in recent years that they are excellent in performance such as internal resistance, short circuit current and discharge characteristics.
A battery case manufactured by a deep draw forming method, DI forming method or DTR forming method comprises a nickel layer or an iron-nickel layer as the surface layer on the inner surface but has a limit in view of the battery performance and improvement has been demanded.
The present invention has a technical subject of providing a battery case excellent in the battery performance and a surface treated steel sheet that can be used suitably to the manufacture of the battery case.